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Functional Neuroanatomy and Biochemistry

Much neuroscience is concerned with identifying functional brain structures through lesion studies. Lesion studies investigate how damaged brain structures yield cognitive-psychological and/or sensorimotor function impairments and help researchers understand the brain’s functional neuroanatomy. An early discovery in functional neuroanatomy, by French physician and anatomist Paul Broca (18241880), was a language center. Broca examined the brains of patients diseased with speech pathologies and frequently found damage in an area now named after him

(Finger 1994, pp. 377-379). Additional functional areas of the brain were discovered during the First and Second World Wars as brain-damaged war victims were analyzed. Our understanding of functional brain anatomy also derives from animal experiments, where deliberate brain lesions have been made and consequences observed.

The growing stock of correlations between mental function and brain physiology has allowed for the construction of brain maps. Brain maps are useful for diagnosing neurological conditions such as stroke—doctors can often infer what brain areas are involved after observing a patient. Moreover, brain scanners reveal brain structures in increasing detail. Scans can show the effects of a stroke or other trauma. Tumors and degenerative disorders (such as Alzheimer’s, Parkinson’s, epilepsy, and white matter disease), as well as others, can often be identified. Emerging higher- resolution scans allow diagnoses that previously required biopsy.

So-called functional scanners reveal active brain areas. By matching active areas with brain maps, it’s possible, under adequate experimental conditions, to make educated guesses about whether a person in a scanner is remembering something, visualizing, listening to music, or reading a text.

We live in an age of visualization with increasingly sophisticated graphic brain models. Brain scanners are as important for neuroscience as telescopes were for Renaissance astronomers. But there is a crucial difference. When Galileo looked through his telescope, he saw moons and other celestial objects—they were simply optically magnified. With brain scanners, we don’t see the brain directly; we see computer-generated visualizations, representing brain structures through electromagnetic properties of atoms, molecules, or gross neural firing patterns, or through radioactive properties of blood-borne tracers, introduced for visualization. To understand what brain visualizations represent, and to what extent and how they might be veridical, requires an understanding of the technology. The fact that brain images are routinely subject to image-postprocessing techniques by researchers makes this task more complicated. Often there is no way of telling what image postprocessing has been performed apart from asking the researchers involved.

Behind modern brain scanning techniques lie truly ingenious applications of molecular chemistry, nuclear physics, quantum physics, and computer-based visualization. The brain is boneless and soft, with little density variation, so x-ray techniques don’t work well. Researchers found alternative ways of visualizing brains—ways to imaginatively exploit fundamental physical properties and mechanisms to reveal brain structure. We will get back to this topic later in this chapter and explore fundamental brain scanning techniques.

Clues to functional brain anatomy also come from microstructurally mapping the brain—its cytoarchitecture. The brain is variegated in terms of cell types and how they combine structurally. Our understanding of the outer layer of the brain—the cerebral cortex—owes much to pioneering cytoarchitectural mappings by German neurologist Korbinian Brodmann (1868-1918). Brodmann’s 1909 work Localization in the Cerebral Cortex[1] (Brodmann and Garey 2010) laid a foundation for functional neuroanatomy by analyzing the cytoarchitecture of the cerebral cortex and illustrating how brain functions (motor, visual, auditory, and language) could be cytoarchi- tecturally mapped into over 50 different areas. His maps and method helped to further functional neuroanatomy. If a brain function cannot be mapped exclusively to one of Brodmann’s cytoarchitectural areas (a rule rather than an exception), this indicates the function is complex and depends on different neural processes.

While there has been progress in functional neuroanatomy during the last century, false claims have also been made. At present, functional neuroanatomy is principally about correlations—how brain activity correlates with cognition—but in the absence of causal explanations, it’s unclear what many of them mean. We know about brain areas that must be operational for a person to experience visual perceptions, but what causes them remains unclear. The same goes for the ability to read the morning paper or ask for a cup of coffee in a cafe—we know something about what brain areas must be intact to do these things, but all the same, we don’t know how anyone comprehends what he/she reads, hears, or says. The causal processes for perception, language use, meaning, cognition, and mental life remain mostly unexplained.

One example of how causal mechanisms behind mental function might be pursued is found within biochemistry. Neurobiologist and Nobel Prize winner Eric Kandel (1929-) has pioneered research on synaptic changes at the molecular level during learning. Kandel believes the mind can be understood analogously to how cell biology was understood in the 1950s (Kandel 2006). We can understand the biology of the mind at the molecular level analogously to how Watson and Crick understood the biology of life—DNA—at that level. Kandel has succeeded in showing how some cases of learning can be better understood through analysis at the molecular level. Moreover, if some cases of learning can be illuminated at this level, why not others? It remains to be seen how far Kandel’s biochemical analysis of the mind goes and how it might be extended to mental capacities other than memory.

  • [1] Brodmann and Garey (2010). Brodmann’s localisation in the cerebral cortex. New York: Springer.
 
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